The solar cells of solar arrays, particularly those designed for use in the outer space environment, are commonly provided with transparent, wavelength-selective coverslides which are adhesively bonded to the active (light-sensitive) faces of the cells. These coverslides attenuate or block transmission to the underlying solar cells of those light wavelengths which tend to heat the cells and degrade the coverslide adhesive. The coverslides transmit to the solar cells substantially only those wavelengths which are best suited for electrical power generation. The adhesively-bonded assembly, comprising a solar cell and coverslide, is commonly referred to as a glassed solar cell or a solar cell stack.
This invention is concerned with the fabrication of such solar cell stacks and, more particularly, with mechanization of such cell stack fabrication. At the present time, the application of coverslides to solar cells, commonly referred to as "glassing" solar cells, is done manually by highly skilled technicians. These manual cell glassing operations are very tedious, time-consuming and costly, and result in relatively high cell and coverglass breakage rates and a relatively high cell stack rejection rate. This is due in part to the nature of the manual glassing operations themselves and in part to the extremely fragile nature of the solar cells and coverslides. Thus, a typical solar cell for spacecraft solar arrays is on the order of 2 cm by 4 cm in size and 200 microns thick. A typical coverslide is made of fused silica or microsheet glass on the order of 150 microns thick and has substantially the same edge dimensions as the solar cells. Obviously, such thin parts are prone to breakage when manually handled. Proper alignment of the coverslides with the solar cells and adhesive bonding of the slides to the cells are also difficult to accomplish manually and, hence, result in a relatively high cell stack rejection rate.
Another problem encountered in manual fabrication of solar cell stacks involves the properties of the coverslide adhesive. Thus, the coverslide adhesive for a spacecraft solar array must be relatively immune to degradation by the radiation in the space environment, must be capable of retaining its strength over the wide temperature range encountered in the space environment, and must be compatible with the materials to be bonded. Suitable coverslide adhesives are quite costly and shortlived. As a consequence, manual cell stack fabrication is not compatible with such adhesives because the time duration of the manual assembly operations results in substantial wasting of the short-lived adhesives. Accordingly, there is a definite need for an improved method of, and means for, fabricating or assembling solar cell stacks.